• Biomass allocation;
  • carbon dioxide enrichment;
  • photosynthesis;
  • Plantago major;
  • relative growth rate;
  • respiration;
  • self-shading

The effect of an elevated atmospheric CO2 concentration on growth, photosynthesis and root respiration of Plantago major L. ssp. major L. was investigated. Plants were grown in a nutrient solution in growth chambers at 350 and 700 μl I−1 CO2 during 7 weeks. The total dry weight of the Co2-enriched plants at the end of this period was 50% higher than that of control plants. However, the relative growth rate (RGR) was stimulated only during the first half of the growing period. The transient nature of the stimulation of the RGR was not likely to be due to end-product inhibition of photosynthesis. It is suggested that in P. major, a rosette plant, self-shading causes a decline in photosynthesis and results in an increase in the shoot: root ratio and a decrease in RGR. CO2-enriched plants grow faster and cosequently suffer more from self-shading. Corrected for this ontogenetic drift, high CO2 concentrations stimulated the RGR of P. major throughout the entire experiment.